Added WifiScanner to manage wifi scanning.
Modified WifiTracker to use WifiScanner instead of WifiManager.
Previously, there was no checking if wifi scanning actually succeeded.
This is solved in this commit, by implementing wifi scanner (broadcast
receiver). Wifi scan checking is now done on two places: on startScan()
request and onReceive() when broadcast is received.

Changed ThirdPartyReceiver intent filter to be registered programatically.
Registering most of intent filters in manifest was disabled in API 26. Apps must now register them programatically.
In case of trackworktime, notification actions stopped working.